The invention relates to ratchet one-way clutch assemblies.
There are various types of one-way clutch assemblies in use today. Such clutch assemblies include sprag-type, roller-type, and pawl ratchet-type assemblies. All of these one-way clutch assemblies work satisfactorily depending upon the particular application in which they are used.
In certain transmissions, increased torque capacity is needed for one-way clutch assemblies. Space constraints also require that the size of the clutch be retained within certain limits. Current one-way clutch assemblies with sprags or rollers are often insufficient to add increased load carrying capacity and still maintain the space constraints.
Pawl one-way clutch assemblies can add increased nominal load capacity for a given package size. The design limits of a ratchet-type pawl clutch assembly are dictated by contact stress between the pawls and the races and/or bending, shear, and hoop stresses generated within the races.
Ratchet clutch assemblies have at least one pawl which acts to lock two notched or pocketed races together in one direction and rotate freely in the other direction. In general, the differences between known ratchet clutch assemblies relate to the control of the movement of the pawls and the effect on that movement by centrifugal forces. Ratchet clutch assemblies are shown, for example, in U.S. Pat. Nos. 2,226,247, 3,554,340, and 5,449,057. Another ratchet clutch assembly is shown in British Patent No. 2116. Some ratchet clutch assemblies utilize stator members as the outer members in place of an outer race member.
Some current pawl clutches are limited in overrunning speed capability and durability for repeated torque loads. Also, stators used for the outer members of clutch assemblies are typically made of cast aluminum which, due to the casting process, do not always provide pawl pocket geometry for proper functioning of the pawl members. A secondary machine operation is typically needed to accurately control the pocket geometry.
It is an object of the present invention to provide improved ratchet one-way clutch assemblies. It is another object of the present invention to provide improved ratchet clutch assemblies which are less expensive and lighter in weight than known assemblies, and yet are comparable in operation and performance.
It is still another object of the present invention to provide ratchet one-way clutch assemblies made of non-ferrous materials, such as plastic or aluminum, which are strong, durable and lightweight. It is a still further object of the present invention to provide ratchet one-way clutch assemblies which utilize springs to place tilting forces on the pawls toward engagement.
It is also an object of the present invention to provide ratchet clutch assemblies which have improved operation at high speeds and have greater durability for repeated torque loads and/or capacity for higher loads. It is a still further object of the present invention to provide ratchet clutch assemblies that minimize or eliminate secondary machine operations in the pawl pockets and thus reduce the time and cost of manufacture and assembly.
The above and other objects of the invention are met by the present invention which is an improvement over known ratchet one-way clutch assemblies.
The present invention provides a ratchet one-way clutch assembly which includes a plurality of pawls positioned in pockets in an outer race member, or in a stator or reactor member. A plurality of corresponding toothed notches are positioned on the outer circumference of an inner race member to mate with the pawls in locking engagement during relative rotation of the outer member and inner race member in one direction. The notches contain teeth on the outside of the race member which are shaped to prevent rotation of the outer member in one direction, but allow freewheeling rotation in the opposite direction. The inside diameter of the inner race member is adapted to mate with and be securely positioned to a support shaft, such as a stationary support shaft of a vehicle transmission.
One or more axial retainer members or devices retain the pawls axially and hold the races together in axial radial alignment, while allowing relative rotation. The retainer devices also act as thrust bearings and can retain required lubrication to prevent excessive wear of the pawls. In accordance with preferred embodiments of the invention, the inner race member has bearing surfaces on one or both sides of the notches which mate with corresponding bearing surfaces on the outer member and the retainer member. This provides additional bearing support which is needed when high radial loads are present.
The pawls have peaks or ridges which mate with pivot ridges or recesses in the pockets in the outer race or stator members. The center of mass of the pawls can be optionally situated or positioned such that when the clutch rotates, the centrifugal force on the center of mass causes the pawls to move toward the engaged or disengaged positions.
Spring members are positioned in the stator or outer race member and adapted to engage the pawls and cause them to be biased in the direction of engagement with the notches in the inner race member. Although various types of spring mechanisms can be used to perform this function, preferably the spring members are wide Z-shaped springs which extend the width of the pawl members.
Preferably, if a stator member is utilized, it is made of a non-ferrous material which is lighter in weight than materials conventionally used for clutch assemblies, particularly outer race members. The nonferrous material can be a metal material, such as aluminum, or a plastic material, such as polyethylene, which meet the durability and strength standards necessary for the application of the clutch assembly. By eliminating the outer race members of clutch assemblies incorporating the pawls and pawl pockets directly into a stator member or other similar member, expenses in materials and in manufacturing procedures are reduced.
The ridge in the outer race pocket is located relative to the center of mass of the pawls in order to control the engaging force. This is necessary for high speed durability. In this regard, it is possible in accordance with an alternate embodiment of the invention to position the center of mass such that the pawl is urged toward the engaged position, or even a xe2x80x9cneutral positionxe2x80x9d neither engaged or disengaged.
Other spring members which can be used with the present invention include garter springs, coil springs and ribbon springs. The spring forces can be applied on a center groove or on one or more side grooves in the pawl members, or the spring forces can act on the pawl members themselves, or in recesses that extend axially along the length of the pawl.
The pivot radius on the pawl members and the mating pivot radius on the outer members are significantly larger than with prior art ratchet clutches. This reduces wear, provides greater durability for repeated torque loads and/or capacity for higher loads, and reduces the cost of secondary machine operations.
bottom surfaces of the pawl members which make contact with the outer periphery or circumference of the inner race members have curved configurations. This allows the clearance between the pawl members and the inner race member to be reduced. Additionally, the radius on the bottom of the pawl members can be made greater than the radius of the mating surface on the inner race members which improves the stability of the pawl when freewheeling.
Protector members can also be used to prevent damage in the pocket area of the outer race members or stator member. Steel or hard inserts can be molded into plastic or composite outer members in the pocket area in order to increase the durability of the components.
The inner race member can also be made of a series of thin plates secured or laminated together. The plates can be of different types, one with notches and the other with bearing surfaces. Stacking mechanisms, such as partial cutout portions (xe2x80x9csemi-perfsxe2x80x9d) can be used to align and hold the stacked plates together before welding, and increase the strength of the inner race member.
The present inventive ratchet one-way clutch assembly has particular use in vehicle transmissions and torque converters and can be used in environments where both races rotate or where one of the races is fixed. The invention can also be used in any mechanism where a positive backstop is desired to prevent undesired reverse or backward rotation, such as in an escalator mechanism or the like.
Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.